In recent years in many developed countries water supply sources have been tending to be deteriorated in quality or purity due to various causes, and moreover addition of chemicals into the water for keeping the water potable can be seen increasing in many water purification plants. This situation tends to increase, in turn, solubility in water of an element or elements of the material for water or hot-water supply tubes or pipes. From the standpoint of keeping water at a high quality level, civilized countries at the present time are under very undesirable circumstances. Zinc plated steel pipes, for example, which have traditionally been used for drinkable or potable clean water supply tend to have a very high concentration of zinc, which often results in a supply of white turbid water. In some regions the zinc coated pipes have been prohibited for use as supply pipes for drinkable clean water. Steel pipes as well have a high dissolution rate of iron, and especially when the water is temporarily staying or stagnant due to an interruption of water supply or some other reasons, the solubility so markedly rises as to make the water brown turbid. Even copper tubes which have been highly appreciated for their durability and workability can not be free from a problem of copper dissolution in water, which varies depending upon nature or quality of the water. In case water is staying in a copper tube the soluble rate of copper ions in the water comes to a high level. The soluble rate sometimes exceeds, for example in Japan, the allowable limit of copper dissolution rate in drinking water (Cu:1.0 ppm) which is stipulated by the Water-Supply Act, No. 11 Order of the Ministry of Health & Welfare, No. 177 Law of Japan enacted in November, 1957, and that still is preventing copper tubes from being widely used as tubes for drinkable clean water supply. It has been urgently required to develop practical or commercial materials for pipes or tubes and instruments usable for clean water supply including drinking water which materials are excellent in preventing the deterioration of the water or in keeping the water potable. The principal object of the present invention is to aim at the provision of such high quality Cu-alloy tubes for the use of water piping and such instruments, to meet this urgent requirement.